The present invention generally relates to a system for monitoring sensors and more particularly relates to a method and a device for monitoring sensors which sense in each case individual reference variables or measured variables relating to a process.
Electronic stability programs of this general type are driving-dynamics control systems for vehicles which are used to assist the driver in critical driving situations during braking, accelerating, and steering, and to intervene where the driver has no direct intervention possibility. The control system assists the driver when braking, especially on a roadway with a low or varying coefficient of friction, on which the vehicle might be no longer controllable due to locking wheels. The system also assists in accelerating, in instances when there is a high risk of spinning of the driven wheels, and also assists in steering the vehicle during cornering, where the vehicle might oversteer or understeer. In total, ESP""s not only improve vehicle response but also improve vehicle safety.
A control system of this type is based on a closed-loop control circuit which, during normal operation of the vehicle, uses standard vehicle control systems to stabilize the vehicle as quickly as possible in extreme driving situations. Sensors used to detect the various driving-dynamics parameters are of special importance as generators of actual values. The precondition for proper control is that the sensors correctly represent the actual condition of the controlled system. This is particularly important in driving stability control operations initiated in extreme driving situations, where a control deviation must be adjusted by the ESP control within a very short time. This is the reason why the ESP sensors (yaw rate sensor, transverse acceleration sensor, steering angle sensor) of an electronic stability program require constant monitoring. The purpose of a corresponding on-line sensor monitoring system is to quickly detect faults in the ESP sensors in order to rule out a faulty control maneuvers which might cause a vehicle condition that is critical in terms of safety.
In view of the above, an object of the present invention is to provide a method and a device for monitoring the output signal of sensors of the above-mentioned type offering the reliability which is imperative especially for an electronic stability program (ESP) for vehicles.
This object is achieved by monitoring the course of the output signals of the individual sensors in a cyclical and sequential manner, comprising the following steps: producing analytical redundancies for a process reference variable or process measured variable being currently monitored from process reference variables and/or process measured variables of a current process, which said variables are not being monitored currently, on the basis of a multi-process model for a normal operational mode, producing residua by subtraction of the produced redundant analytical redundancies from the currently monitored process reference variable or process measured variable, evaluating the residua by means of a residua evaluating function and comparing the evaluated residuum with a predetermined threshold value and producing a fault message when the residuum reaches the threshold value for at least one predetermined monitoring time.
Further, this object is achieved by a first device for calculating analytical redundancies for a currently monitored process reference variable or process measured variable from currently not monitored process reference variables and/or process measured variables of a current process by means of a multi-process model for a normal operational mode, a second device for producing residua by subtraction of the calculated redundant analytical redundancies from the currently monitored process reference variable or process measured variable, a third device for evaluating the residua with a residua evaluating function, a fourth device for producing a threshold value, as well as a fifth device for comparing the evaluated residuum with the threshold value and for producing a fault message when the residuum reaches the threshold value for at least one predetermined monitoring time.